I doubt anybody is going to give away their favorite beach. Perhaps, the better way to ask the question is: what to look for in a holiday destination? - - and then do your own research.
Here are my initial thoughts:
I can tell you that it would be best to avoid rough water (Atlantic side of Caribbean Islands) if you are wading. It is not much fun getting picked up and flipped over - usually right after getting a nice gold signal. I use dive weights if there are large waves which helps keep my feet on the bottom when it is a bit rough. Avoid pay beaches - unless you confirm beforehand that they will allow detecting. In fact, look up if the beaches/water are public or private (the laws differ on each island). Decide if you want to stick to one resort or drive to multiple spots on the island - if one resort, then it is rather important to find the right one. Also confirm if the beach is shallow for a ways out or drops off fast - this will tell you how much detectable ground there is. New one for me - Find out if they dredge the sand annually (I was at a place last year that did not have much and I found out late in the trip that it gets dredged). If you scuba, get a resort with an onsite shop and if you solo, confirm prior they will rent to you. A good idea to look online at the pictures of the beach you intend to detect. Lots of videos and pictures posted nowadays. One last thought, I have done better where the clientele were European/South American vs American/Canadian. I suspect beaches with lots of Canadians/Americans have a few of us with detectors and they have been hit more often.
As for S. Florida being cold, you should check the water where I am right now. There is already an inch of ice.
